This invention relates to heat processing sealed containers, and more particularly to prevention of container distortion and protection of container seal integrity during heat processing.
Heat sterilization of sealed food containers such as glass jars or flexible pouches generally requires an overriding pressure in the sterilizing environment to keep the containers from rupturing or the container lids from being pushed off due to the usual rise of internal pressure within the containers caused by the processing temperatures. To prevent destruction of the seal integrity it has been necessary to either maintain a positive pressure differential between the interior of the heat processing chamber and the interior of the container or to introduce air together with the heat transfer medium, such as saturated steam, into the processing chamber. The disadvantages associated with maintaining the positive pressure differential relate to system complexity and the disadvantages associated with introducing air with the heating medium to obtain the overriding pressure accrue from a loss of heat transfer efficiency due to the insulating property of the non-condensible gas (air) as well as condensation inefficiencies when the air and steam mixture is passed from the heat processing chamber to a condenser for recovery and return to the system.
U.S. Pat. No. 4,066,399, Gunther, relates to an enclosed sterilizing chamber in which articles to be sterilized are placed. The atmosphere within the chamber is humidified to a predetermined degree prior to introduction of a sterilizing gas. The degree of humidification is obtained by mixing water and an organic solvent in known proportions and atomizing the mixture as it is injected into the chamber. The proper degree of humidification is sensed by a pressure sensor, since relative humidity in the chamber is directly proportional to pressure, and injection of humidifying mixture is stopped. Ethyl alcohol is one organic substance mentioned by Gunther as appropriate for obtaining the desired chamber humidity.
U.S. Pat. No. 3,404,946 issued to Reis discloses apparatus for sterilizing articles within enclosed containers. The containers hold ethyl alcohol which is used as an antiseptic fluid. Steam is introduced into a chamber surrounding the containers to provide a heat source. The pressure of the volatile alcohol in the containers rises faster than the pressure surrounding the containers. The internal container pressure rise presents a danger of container explosion and therefore air pressure is introduced into the chamber to counteract the increased internal container pressure.
U.S. Pat. No. 3,986,382, Smorenburg, also discloses a thermal sterilizing system for filled containers where air is used to provide the overriding pressure to prevent container deformation or rupture.
Kotarski et al. U.S. Pat. No. 3,093,449, also relates to a system wherein steam is used to provide heat at the sterilization temperature in a sterilization chamber and compressed air is introduced into the steam mass to provide an overriding pressure in the chamber for the aforementioned purpose. These patents seem to typify the prior art over which the subject disclosure provides an advance.